Automatic motor-starter.



No. 874,531. PATENTED DEC, 24, 1907.

' W. C. OBRIEN.

AUTOMATIC MOTOR STARTER.

APPLICATION FILED OGTZS1 1905.

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AUTOMATIC MOTOR STARTER.

APPLICATION FILED 0CT.23.1905.

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TH E mamas APPLICATION FILED 0012s, 1905.

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UNITED STATES PATENT OFFICE.

WILLIAM G. OBRIEN, OF BALTIMORE, MARYLAND, ASSIGNOR TO MONITORMANUFACTURING E AUTOMATIC MOTOR-STARTER.

Specification of Letters Patent.

Patented Dec. 2%, 1907.

Application filed October 23. 1905. Serial No. 284,105.

To all whom it may concern:

Be it known that I, WILLIAM G. OBninn, a citizen of the United States,residing at Baltimore, in the State of Maryland, have invented certainnew and useful Improvements in Automatic Motor Starters, of which thefollowing is a specification.

The purpose of this invention is to provide an automatic starter forelectric motors which will operate to cut the starting resistance out ofthe ari'nature circuit as the motor acquires speed, without the use ofdash pots or other mechanical retarding devices.

In the accompanying drawingFigure 1 is a diagrammatic view showing asimple form of starter, having but one resistance section, and havingtwo switches in the circuit which shunts the resistance, the movableparts being shown in their normal positions, and the solenoid beingshown in section Fig. 2 is a similar view showing the positions of" themovable parts immediately following the closing of the line switch; Fig.3 is a similar view showing the positions of the movable parts of thestarter while the motor is running under normal conditions Fig. 4. is adiagrammatic view showing a starter having a series of steps or sectionsin the starting resistance, and two switches for each shunt circuit, themovable parts being shown in their normal positions .in full lines Fig.5 is a similar view of the starter shown in Fig. 4, the movable partsbeing shown in full lines in the positions which they occupy immediatelyalter the closing of the line switch, when the full starting current isflowing through-the armature circuit; Figs. 6, 7 and 8 showdiagrammatically a starter having a single resistance section with twomovable switch members in the circuit which shunts the resistance, bothmembers forming parts of the same switch; Fig. 8 is a detail showing a.modification of the'starter illustrated in Figs. 6, 7 and 8, the movableswitch members in Fig. 8 being arranged to engage a fixed member commontoboth.

The starter illustrated in Figs. 1, 2 and 3, having but a single step inthe starting resistance, is especially suited for motors of the smallersizes, such as those commonly used in shops for operating machine tools,although it may be used for meters of larger sizes which. start withoutload.

Referring to Figs. 1, 2 and 3, L and L indi cate the conductors of adirect current constant potential line circuit, and S indicates rangedadjacent to the magnet H.

of the armature extends from the conductor 3 through a conductor 5,thence through the coils 6 ol a holding magnet II, and thence by aconductor 7 to the coils c of a solenoid O. From the coils of thesolenoid the circuit ex tends through a starting resistance R and thencethrough a contact block 8. This contact block is connected to one brushof the armature by a conductor 9 and the other brush of the armature, asshown, is connected to the conductor 4. lenoid, as well as the startingresistance, are thus connected in series with the armature of the motor.

The solenoid is provided with a core 10 having a contact shoe 1 1pivotally connected thereto so that the said shoe may adjust itsell tothe surface of the contact block 8 and make a good electrical connectiontherewith when the shoe rests upon the block, as shown in Figs. 1 and 3.The parts 8 and 11 constitute the two members of a normally closedswitch S which is opened by the lifting of the solenoid core when thecurrent at starting ex ceeds the maximum current which the motor isintended to carry under normal conditions, but remains closed if thecurrent at starting is not in excess of the normal current. The switchmember 11 is connected in a circuit, which, when said circuit is closed,forms a shunt around the terminals of the solenoid windings and theresistance R. This shunt circuit, however, is normally open. As shown,the switch member 11 is connected by a flexible conductor 12 and wire 12to one member 13 of a normally open switch S, the other member 14: beinga clip which is connected. to the solenoid terminal 7 and ar- The switchmember 13 normally rests upon a stop 2 and is located above a rod 15secured to the solenoid core 10. This red, as shown, is preferably madeof insulating material, although it may be of metal.

vi hen the line switch S is closed to start the motor the magnet IIwhich responds to large or small current strengths will attract itsarmature and close the switch S. If the current lilowing in the armaturecircuit is above normal, the core of the solenoid will rise and open theswitch S. As the magnet The coils of the so- I the line switch is againopened.

and solenoid are simultaneously energized, the switch S will be openedbefore the switch S closes. As long as the armature current remainsabove a predetermined quantity, the solenoid core will remain in itsraised position, as shown in Fig. 2, and the shunt circuit 12, 12 aroundthe resistance and solenoid coils will remain open. falls to normal, asthe motor armature acquires speed, the solenoid core will drop and closethe switch S, while the switch S will remain closed, as shown in Fig.The shunt circuit will then be complete, and the resistance and solenoidcoils will be short circuited while the motor is running and until Whenthe line switch is opened to stop the motor, the magnet H becomesdeenergized, and the switch-member 13 falls to open position, thusleaving the shunt circuit open, so that when the line switch is againclosed the same suecessive operations will take place.

IFhile the magnet II closes the switch S each time the line switch isclosed, whether the current flowing be large or small, the solenoid isarranged to move its core and open the switch S only in case thearmature current, at starting, is above a predeterminedquantity,-usually but not necessarily the maximum current which themotor is designed to continuously carry. This predetermined quantity isherein referred to for convenience as the normal armature current. It,therefore, the current does not exceed this predetermined quantity whenthe line switch is closed to start the motor, the switch S will closeand the switch S will not open, and the resistance and solenoid will beimmediately cut out, the current flowing directly to the motor throughthe shunt circuit as soon as the switch S closes.

Ordinarily, the current at starting is sullicient to lift the solenoidcore, and, where the motor always starts with a current above thecurrent required to move the solenoid core, the core may be used tooperate both switches, by arranging the switch member 13 above the rod15, as shown, so that the rod will move said member upward into positionwhere it will be acted upon and held by the magnet. In any case, wherethe current is above the predetermined quantity, the switch S will openbefore the switch S closes, so that the resistance cannot becomeshortcircuited until the current falls to normal.

In Figs. a and 5 I have shown a starter having a resistance arranged insections or steps with a series of eleetro-magnetically operated devicesfor short circuiting these sections successively, the principle ofoperation being the same as in the previously described figures. Inthese views C, C C and C, indicate solenoids having cores arranged torespond to successively greater excess currents hen the current lcnoidhaving a core which responds to currents of any strength. The solenoidsC to C inclusive are substantially the same as the solenoid C in Figs,1, 2 and 3, and the solenoid ll corresponds in function to the magnet IIof said figures. As shown in Fig. -l, the coils of the various solenoidsare connected in series with one another and with the resistancesections It to R" inclusive, and the motor armature (1. Thus the lineterminal 1 is connected to one terminal of the coils of the solenoid IIby a conductor 25 and the other terminal of said coils is connected by aconductor 16 to the coils of the adjacent solenoid C". From these coilsthe armature circuit extends by conductor 17 through one section R ofthe resistance and thence to the contact block or switch member 8 of anormally closed switch S". From said contact block the armature circuitextends through a conductor 16 to the coils of thenext solenoid C in theseries and thence by conductor 17 to the next section It of theresistance and thence to the contact member 8 of a normally closedswitch In the same manner the circuit extends through successivesolenoid coils C and C, resistance sections R and R and members 8 ofswitches S and S through the conductors 16 17 and 16, 17". The member 8of the normally closedswitch S is connected by the conductor 18 to onebrush of the armature a and the opposite brush is connected by theconductor a to the line terminal 2. The field f of the motor isconnected to the line terminal 1 by a conductor 3. The normally closedswitches S to S inclusive are the same as the normally closed switch Sin Figs. 1, 2 and 3, and the switch. members 11 of these switches areconnected respectively by separate conductors 12 to 12, inclusive, toseparate members 1a to 14, inclusive, which form parts o'l normally openswitches S The core 3* ol the solenoid II carries at its upper end acontact plate or switch member 13", adapted, when the core is movedupward, as shown in Fig. 5,, to connect each of the low resistancecircuits 12 to 12 inclusive, with the line t erminal 1 through aflexible conductor 19 which is attached to the member 13 and connectedto the conductor 25. The solenoid II is made so that its core will moveupward when either a small or a large quantity of currentis llowingthrough its coils, and in order to make this solenoid sensitive to smallcurrents the weight of the core 13' may be partly counterbalanced bysprings 20. Yhile the solenoid II will respond to current 01" any volumewhich may flow in the armature circuit, and thus cause the switch member13" to close the normally open switches in the shunt circuits12 ,12 thesolenoids C to C", inclusive, respond only to currents which are inexcess of the normal current which it is inin the armature circuit andII indicates so- 1 tended that the motor shall carry, and thesesolenoids, in succession, respond to successively greater currentstrengths. These solenoidsrnay be constructed. to act under variouscurrent strengths in any well-known way. For convenience'ol illustrationI have shown the solenoids ofui'iii'orm, size, but with successivelylarger weights to upon rods '15 which are attached to cores 10, so thatthe solenoids will operate With successively greater current strengths.

InFig. 5 the circuits are the same as in Fig. l, except that instead ofconnecting the coils of the solenoid H in series with theselenoidsC to C.inclusive, 1 have shown, as a modification, the coils of the solenoid.H eon nected directly to the wires 3 andv 4 by conductors 2i and 22,and. the wire 16, connected to the coil C, is also connected. to theconductorS. It is immaterial whether the coils of the solenoid H areconnected across the line, as shown, or in series with the othersolenoids so long as current is admitted to all of the solenoids at thesame time.

In operation whenthe line switch S is closed, the current flows throughthe coils of all of the solenoids and. through. the starting resistanceto the armature. hether the current immediately following the closure ofthe line so itch, .is large or small, the solenoid core 13 moves upwardand the snitch member 133 actuated thereby, engages the switch members14* to 14 inclusive, and connects the shunt circuits li -12 to the lineterminal '1. ll" the current flowing in the armature circuit is not inexcess of the normal, no one of the solenoids C to C inclusive will moveits core, and, 'tl'iere'l'ore, the current will flow directly to thearmature from the switch con- 1.4 through. the shunt circuit 12 and. .hS. The core 13 will remain in is raised position long as the line switchis closed, and it will be seen that all of the resistance, well as thecoils oi the solenoids C to O inclusive, it ill be short circuiiedthrougl'i the conductor 12 If, however, the starting current should beonly slightly in excess of the normal, at the time the line switch isclosed, the core of the solenoid C will lift simultaneously n ith theupward movement ol'- the core of the magnet H and the normally closed.switch S will be opened before the switch. member 13 closes the circuitthrough the conductor 12. The current, there'lore, instead. of flowingthrough the shunt circuit 12 to the armature will then flow from thecontact 14 through shunt circult l2, S\\1't0l'i S", conductor 16, cellsof sorent is great enough to actuate the solenoid C it will also actuatethe solenoidC and the arma ure current n ill then flow through shuntcircuit 12 solenoids C and C, and resistance sections R and R and. thetwo sections R and R of the resistance it ill be maintained in series itith the armature until, as the current Falls, the core of the magnet (1'w ill first drop, thus closing the shunt circuit 12" and cutting out theresistance section R and then, iih a further fall in current, the coreof" the solenoid. C will drop, cutting out the resistance section R.

If the current at starting is great enough to actuate all of thesolenoids C to C inelusive, these v. ill open the switches S to Sinclusive, before the shunt circuits 12 to 12 inclusive are completed atthe su itches 14 to 14 inclusive, and all of the resistance sections Rto R inclusive, n ill thus be in series with the mo; or as shown in Fig.5. As the current falls to normal, it will be obvious that uthe solenoidcores which operate the normally closed. switches v ill drop insuccession, from left to right in the draa ing, thus cutting out theresistance sections gradually and successively according to the rate atwhich the current in the armature circuit diminishes.

The electro-magnetic device H for closing the normally open sr. itehesin the shunt circuits may be used in connection with as many of thedevices for operating the normally closed s1 itches as may be desired.It w ill be noted that the starter requires no mechanieal retardingdevices and that it affords positive protection to the motor fromexcessive currents in starting, since the solenoids prevent shortcircuiting of the resistance as long as the starting current is abovethe normal.

In Figs. 6 to 8 inclusive, I have illustrated starters operating uponthe same principle the previously described. figures, but in Figs. 6 to8 inclusive, there is only one sv. itch in each shunt circuit, thisswitch being normally open. This switch, however, has two movableswitclrmembers, one normally in position to be engaged. by the other toclose the low resistance shunt circuit, and movable from said. position,which may be called its closed position, only when the starting currentin the armature is above a predetermined quantity, and the other memberbeing normally in position to maintain the shunt circuit open andmovable from said position, which may be'called its open position, intoposition to engage, or to be engaged by, the first mentioned. membereach time the line switch is closed.

Referring to Figs. 6, 7 and 8, which rep resent a starter, suitable forthe small sizes of motors in which the resistance is cut out at a singlestep, C indicates an ordinary solenoid. arranged in the armature circuitof the motor M and adapted to move its core 10 upward only When thecurrent at starting is in excess of the normal current which the motoris designed to carry, and II indicates a solenoid sensitive to large orsmall currents and adapted to move its core 13 upward each time the lineswitch is closed and to hold said core in its upper position as long ascurrent is passing through the motor. As shown one terminal of thesolenoid (3 is connected to the line terminal 1 and the other terminal27 is connected to one terminal of the resistance It. From theresistance R the armature circuit extends through conductor 28 to thecoils 72 of the sensitive solenoid and thence by conductor 29 to thearmature a of the motor. The conductors 3 and 4 are connected to themotor in the same manner as in the previously described figures. Inthese figures the core 10 of the solenoid C, which is arranged directlyabove the core of the solenoid H, forms part of the shunt circuit which,when the motor is in operation, is completed around the coils of thesolenoid (land the starting resistance B. As shown a rod 15 ofnonmagnetic metal is attached to the core 10 and carries a stop 30 whichlimits the downward movement of the core. The core is electricallyconnected to the terminal 26 by a flexible conductor 31 which, as shown,is attached to the stop 30. The core 13 of the magnet II also hasconnected to it an up wardly extending rod 13, of non-magnetic materialwhich may be either metal or a nonconductor, and this upward extensioncarries a block S of conducting material which is electrically connectedto the conductor 28 by a flexible conductor 32. The block 8" forms onemember of a normally open switch S and also serves as astop to limit thedownward movement of the core 13 The part 11 connected to the core 10forms the other member of said normally open switch.

Fig. 6 represents the normal positions of the parts, when the lineswitch S is open and the motor is stopped. In this position it will benoted that the switch S is open. When the line switch S is closed tostart the motor, if the current in the armature circuit at the momentwhen said switch is closed is in excess of the normal armature current,the cores of both solenoids will be drawn up simultaneously, as shown inFig. 7, and the switch S will, therefore, remain open until the currentin the armature current falls to normal, as the motor acquires speed,when the core of the solenoid. C will fall and the switch member 11 willengage the switch member 8, as shown in Fig. 8. As soon as the switch Sis thus closed. current will fiow through the conductor 31, red 15,core10, switch S and conductor P2, thus short circuiting the coils of thesolenoid C and the resistance B. As the solenoid II responds to eitherlarge or small currents its core will be held in its upper position aslong as the line switch is closed and current is flowing through themotor. It will, therefore, support the core 10, as shown in Fig. 8,after the coils of the solenoid C have been short circuited and thecurrent will continue to flow through the low resistance shunt circuituntil the line switch S is opened and the sensitive solenoid I-I therebydeener ized, when the core of said latter solenoid will drop into theposition shown in Fig. 6, thus leaving the shunt circuit open.

If the current in the armature circuit at the same time when the lineswitch is closed should not exceed the normal armature current, the coreof the solenoid C will not be lifted but the core of the solenoid IIwill move upward carrying the switch member 8 into engagement with theswitch member 11, as shown in Fig. 8, thus closing the shunt circuit andshort circuiting the coils of the solenoid C and the starting resistanceR. The starting resistance will, therefore, be out immediately out ofthe circuit by the device described if the motor takes normal current,or less, at starting; but if the current is in excess of the normal thestarting resistance will not be cut out until the armature current fallsto normal. It is immaterial whether the sensitive solenoid H beconnected in series, as shown, or across the line so long as the twosolenoids are simultaneously encrgized when the line switch is closed.

In Fig. S I have shown a fixed stop of conducting material which isinterposed between the two movable switch members 8 and 11. This stepconnects the two movable switch members electrically when the motor isin operation, and it prevents the lower member 8 from striking the uppermember and causing the upper member to be thrown upward when thestarting current is insufficient to cause the upper solenoid to lift itscore. Under these conditions the lower movable member moves up, asindicated in dotted lines, into engagement with the stop or stationary s'itch member, on which the upper movable member rests. This step isdesirable for these conditions of small starting current, but, where thecurrent is always sufficient to lift both movable switch members, thelower one comes to its upper position and is strongly held there, asshown in Fig. 7, forming a firm support which is not affected by thefalling of the upper member upon it, and with the larger current thestationary stop or switch member is not essential.

In the various forms of my invention shown the starting resistance isnormally arranged in series with the armature so that the armature isprotected by the resistance and the full starting current can flowthrough the armature as soon as the line switch is closed to completethe motor circuits.

.Yhether the normally closed switch member 111 a shunt circuit moves toopen position or Git eraser remains in closed position depends upon thequantity of starting current flowing through the armature circuit in theinterval between the closing ol the line switch and the closing of thenormally open. switch in said shunt circuit. If this quantity is above apredetermined value during said interval, the solenoid controlling thenormally closed switch member moves said member to open position beforethe normally open member reaches the closed position, and it below saidvalue the normally closed member remains stationary and the resistancesection and solenoid coils are at once short circuited by the completionof the shunt circuit through the normally open member, which is moved toclosed position each time the line switch is closed. here the startingcurrent,that is, the current which flows through the re sistance to thearmature to start the motor,-is not in excess of the predetermined safequantity, no time element enters into the operation of short-circuitingthe resistance other than the brief interval required for the normallyopen switch. to be moved. into closed position by its magnet.

Having thus described my invention what I claim and desire to secure byLetters Patent of the United. States is 1. In an automatic starter forelectric motors, a starting resistance in the armature circuit, anormally open low-resistance circuit in shunt to said startingresistance, two movable switch members in said shunt circuit, anelectroanagnetic device adapted to move one of said members to closedposition each time the line switch is closed, and an electro-magneticdevice adapted to move the other member to open position only when thearmature current at starting is above a predetermined quantity.

2. In an automatic starter for electric m0- tors, a starting resistancein the armature circuit, a normally open low-resistance circuit in shuntto said starting resistance, two movable switch members in said shuntcircuit, an electromagnetic device adapted to move one of said membersto closed position each time the line switch is closed, and anelectro-niagnetic device adapted to move the other member to openposition only when the armature current at starting is above apredetermined quantity, said electro-niagnetic devices being connectedso as to be simultaneously energized when the line switch is closed.

3. In an automatic starter for electric motors, a starting resistance inthe armature circuit, an electro-magnetic device having coils in saidcircuit, a normally open low-resistance circuit in shunt to said coilsand resistance, two movable switch members in said shunt circuit, oneadapted to be opened by said device when the armature current atstarting exceeds a predetermined quantity, and an electro-magneticdevice arranged to move the other member to closed position each timethe line switch is closed.

4. In an automatic starter for electric inotors, a starting resistancein the armature circuit, an electromagnetic device having coils in saidcircuit, a normally open low-resistance circuit in shunt to said coilsand resistance, two movable switch members in said shunt circuit, oneadapted to be moved to open position by said device when the armaturecurrent at starting exceeds a predetermined quantity, and anelectro-magnetic device arranged to move the other member to closedposition each time the line switch is closed.

5. In an automatic starter for electric motors, a starting resistance inthe armature circuit, an electro-magnetic device having coils in saidcircuit, a normally open low-resistance circuit in shunt to said coilsand resistance, two movable switch members in said shunt circuit, oneadapted to be moved to open position by said device when the armaturecurrent at starting exceeds a predetermined quantity, and anelectro-magnetic device responsive to currents of less strength thansaid. predetermined quantity adapted to move the other switch member toclosed. position.

6. In an automatic starter for electric motors, a starting resistancefor the armature circuit, an elcctro-magnetic device having windings insaid circuit, a normally closed switch and a normally open switcharranged. in a low-rcsistance circuit adapted to shunt said. resistanceand windings, said device being arranged to open said normally closedswitch only when the armature current at starting is above apredetermined quantity, and electro-magnetically operated means adaptedto close said normally open switch after current has been admitted tosaid windings.

7. In an automatic starter for electric mo tors, a starting resistancefor the armature circuit, an electro-magnetic device having windings insaid circuit, a normally closed switch and a normally open switcharranged in a low-resistance circuit adapted to shunt said resistanceand windings, said device being arranged to open said normally closedswitch only when the armature current at starting is above apredetermined quantity, and an electro-magnetic device, responding tosmall current strengths arranged to close said normally open switchafter current has been admitted to said windings.

8. In an automatic starter for electric motors, a resistance arranged inthe armature circuit, a low resistance circuit in shunt to said startingresistance, a normally closed switch and a normally open switch in saidshunt circuit, and electromagnetic means for first 0 )ening saidnormally closed switch and then c osing said normally open switch whenthe current is turned on.

9. In an automatic starter for electric motors, a starting resistance inthe armature circuit, an electro-magnetic device having cells m saidcircuit, a low resistance circuit in shunt to said startmg resistanceand coils, a 7

normally closed switch in said shunt circuit adapted to be opened bysaid electromagnetic device when the starting current in the armaturecircuit exceeds a predetermined quantity, a normally open switch in saidshunt circuit and means for closing said latter switch after thenormally closed switch has opened.

10. In an automatic starter for electric motors, a starting resistancein the armature circuit, an electro-magnetic device having coils in saidcircuit, a low resistance circuit in shunt to said coils and saidstarting resist ance, a normally closed switch in said shunt circuitadapted to be opened by said device when the armature current atstarting is in excess of a predetermined quantity, and a normally openelectro-magnetically con trolled switch in. said shunt circuit adaptedto close after the normally closed switch has opened and to remainclosed while the motor is in o aeration.

11. 11 an automatic starter for electric motors, a starting resistancein the armature circuit and an electro-magnetic device having coils insaid circuit, alow resistance circuit in shunt to said startingresistance and coils, a normally closed switch in said shunt circuitadapted to be opened by said device when the starting current in thearmature circuit exceeds a predetermined quantity, and anelectro-magnetically controlled normally open switch in said shuntcircuit arranged to close when current is admitted to the armature.

12. In Ian automatic starter for electric motors, a starting resistancein the armature circuit, a solenoid having windings in said circuit, alow resistance circuit in shunt to said windings and startingresistance, a core adapted to be lifted by said solenoid when thestarting current in the armature circuit exceeds a predeterminedquantity, and to fall by gravity when the current falls to normal, anormallygclosed switch in said shunt circuit adapted to be opened by theupward movement of said core, and a normally open switch in said shuntcircuit arranged to close after said core has moved upwardly, and meansfor holding said normally open switch in closed position while the motoris running.

13. In an automatic starter for electric motors, a series of resistancesections in the armature circuit, a plurality of electro-magneticdevices each having windings in said circuit, low-resistance circuitsarranged to shunt said resistance sections and windings, a normally openswitch and a normally closed switch in each shunt circuit, each of saiddevices being adapted to open one of said normally closed switches, andsaid devices being arranged to respond in succession to successivelygreater quantities of starting current, and electro-1nagneticallyoperated means adapted to close said normally open switches aftercurrent has been admitted to said windings.

141. In an automatic starter for electric motors, a series of resistancesections in the.

armature circuit, a plurality of electro-magnetic devices each havingwindings in said circuit, low-resistance circuits arranged to shunt saidresistance sections and windings, a normally open switch and a normallyclosed switch in each shunt circuit, each of said devices being adaptedto open one ol said normally closed switches and said devices beingarranged to respond in succession to successively greater quantities ofstarting current, and an electro-magnetic device responding to smallcurrent strengths, arranged to close said normally open switches aftercurrent has been admitted to said windings.

15. In an automatic starter for electric motors, a starting resistancenormally arranged in the armature circuit, an electromagnetic devicehaving its windings in said circuit, a normally open low resistancecircuit in shunt to said resistance and windings, two indepemlentlymovable switch members in said shunt circuit, one oi said members beingnormally in closed position and movable by said device to open positiononly when the starting current is above a predetermined quantity, theother of said members being normally in open position, and anelectromagnetic device for moving said latter member to closed positioneach time current is admitted to the armature.

16. In an automatic starter for electric motors, a starting resistancearranged in series with the armature, an electromagnetic device havingits windings in series with said resistance and armature, a normallyopen low resistance circuit in shunt to said resistance and windings, aswitch member in said shunt circuit normally in closed. position andmovable by said device to open position only when the starting currentexceeds a predetermined. quantity, aswitch member in said shunt circuitnormally in open position, and means for moving said latter member toclosed position each time current is admitted to the armature.

17. In an automatic starter for electric motors, a starting resistanceand a solenoid arranged in series with the armature, a normally open lowresistance circuit in shunt to said starting resistance and solenoid, aclosed position each time current is admitted switch member-in saidshunt circuit, norto the armature.

mally in closed position, and adapted to be In testimony whereof I afiiXmy signature, moved to open position by said solenoid only in presenceof tWo Witnesses. when the starting current is above a prede- WILLIAM C.OBRIEN. termined quantity, a switch member in said shunt circuitnormally in open position, and means for moving said latter member intoWitnesses:

HOWARD E. CRUsE, MAURIOE B. OARLEN.

